monitoring of recent mass movement activity in anthropogenic … · 2020. 7. 15. · j. burda et...

Nat. Hazards Earth Syst. Sci., 11, 1463–1473, 2011www.nat-hazards-earth-syst-sci.net/11/1463/2011/doi:10.5194/nhess-11-1463-2011© Author(s) 2011. CC Attribution 3.0 License.

Natural Hazardsand Earth

System Sciences

Monitoring of recent mass movement activity in anthropogenicslopes of the Krusne Hory Mountains (Czech Republic)

J. Burda1,2, L. Zi zka1, and J. Dohnal2

1Brown Coal Research Institute j.s.c., Most, Budovatelu 2830, Czech Republic2Faculty of Science, Charles University in Prague, Praha 2, Albertov 6, Czech Republic

Received: 16 September 2010 – Revised: 7 April 2011 – Accepted: 26 April 2011 – Published: 19 May 2011

Abstract. Recent mass movements currently comprise oneof the main morphogenetic processes in the extensive anthro-pogenic relief of the foreground of the Krusne Hory Moun-tains in the Czech Republic. These mass movements resultin several types of deep-seated slope failures, depending onthe type of movement and the water saturation of the land-slide material. This paper presents the results of a detailedgeomorphic survey and orthophotograph analysis combinedwith geodetic monitoring data in an area affected by open-pit coal mining. An interdisciplinary approach has enabledan in-depth review of both the dynamics and developmentof recent slope failures. The article describes deep-seatedlandslide complex in this part of the foothills of the KrusneHory Mountains. At the study site, mass movements occurin thick colluvial mantle and weathered Tertiary claystones.The main factors influencing their development include rain-fall culminations, groundwater flowing from the valley ofSramnicky Brook and former slope failures. All of the slopefailures that have occurred here have originated at formerslope failure sites.

1 Introduction

The northwest part of the Czech Republic includes regionswith a long tradition of brown coal mining. At the begin-ning of the second half of the 20th century, lignite miningwas conducted in large open-pit mines. In many cases, thismining takes place in specific geological and geomorphic set-tings. The study area is located at a site where the side slopesof the Ceskoslovenska Armada (CSA) open-pit mine passfrom the Mostecka Panev Basin into the crystalline massifof the Krusne Hory Mountains (Fig. 1). Up until 2009, the

Correspondence to:J. Burda([email protected])

CSA open-pit mine was the deepest mine in the Czech Re-public, with a depth of about 200 m. A high anthropogenicslope passes smoothly into the steep slopes of the KrusneHory Mountains and involves a continuous 700 to 800 m highslope. Therefore, in connection with the intensive unloadingof the basin and considering specific geological conditions(Marek, 1983; Horacek, 1994), the question of foothill slopeinstability arises, particularly around the Jezerı Castle, whichis situated on a tectonically broken crystalline slope abovethe CSA open-pit mine. To prevent relaxation of the crys-talline massif around the Jezerı Castle, a protective pillar1

was left under a problematic part of the slope (Fig. 1b). Asimilar protective pillar was projected under Jezerka Moun-tain (about 2 km to the west), but due to landslides, the pillarwas significantly reduced in the 1980s and 1990s. Conse-quently, the stability of the Jezerı protective pillar has beencontinuously monitored at 45 stabilized geodetic points by anautomated total station since July 2005 (Stanislav and Blın,2007). This kind of geodetic method is often used in moni-toring open-pit mines (Brown et al., 2007); in northwest Bo-hemia it has been used since 1997 (Vetrovsky, 2002).

Many authors (Kalvoda et al., 1990, 1994; Rybar andNovotny, 2005; Rybar, 2006; Burda, 2010; Burda andVil ımek, 2010) point out that the stability of this anthro-pogenic slope is complicated by slope steepness, geologicaland geomorphic settings, as well as climatic factors. Thisstudy presents the results of field mapping, aerial orthopho-tograph interpretation, geophysical investigation and geode-tic monitoring of theCSA slopes, revealing the dynamics ofthese mass movements. The objective of this study is thegeomorphic interpretation of geodetic monitoring as well asconfirmation of the influences of climatic factors on slopestability. Comparison with the results of geodetic monitor-

1A large block of solid material left unworked near the slope(in this case about 500 million m3 of original, undisturbed materialabove the coal seam)

Published by Copernicus Publications on behalf of the European Geosciences Union.

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1464 J. Burda et al.: Monitoring of recent mass movement activity

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Figure 1 3

General topographic and geological overview (A); aerial view of the study site; position of the 4

protective pillar and surrounding overburden slope – dashed yellow lines (foto: J. Burda, 5

2010) (B). 6

Fig. 1. General topographic and geological overview (A); aerial view of the study site; position of the protective pillar and surroundingoverburden slope – dashed yellow lines (foto: J. Burda, 2010) (B).

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Figure 2 3

Schematic geological cross-section through the edge of the Most Basin and Krušné Hory

Mountains (modified after: Marek, 1983).

Fig. 2. Schematic geological cross-section through the edge of theMost Basin and Krusne Hory Mountains (modified after: Marek,1983).

ing and data sets from the Jezeı meteo-station offers a uniqueopportunity to study the influence of climate factors on massmovement dynamics.

2 General geological and geomorphic settings

The study area (about 1.5 km2) is located at the foot of asoutheast facing slope of the Krusne Hory Mountains madeup of a portion of the Katerinohorska Klenba (vault) in thephysiographic province of the Krusne Hory Mountains andthe Mostecka Panev (basin).

The Katerinohorska Vault has a flat anticline structure,whose axis approximately follows a west-east direction. Thecore of this vault consists of orthogneiss, which belongs toa packaging series of crystalline rocks (Fig. 1). Accordingto Marek (1983), the foliation surface is fan-like with an in-clination of 50◦ to 70◦. Crystalline rocks are characterized

by the considerable density of fault zones in a NW-SE di-rection in the study area (Skvor, 1975). These fault zonesoccur even in the highest area of the massif and disrupt thebedrock, creating a system of blocks (Fig. 2). To prevent thebedrock from relaxing, during unloading after the excavationof the basin’s sediments, a protective pillar was placed underthe most problematic part of the slope.

The sediments of the Mostecka Basin consist of the under-lying complex2 (mainly lower Miocene sandy-clays), coalseams and the overlying complex (upper Miocene clay-stones). The underlying complex is made up of sedimentssituated under the base of the coal seams. Stratigraphically,it is a heterogeneous unit with various Tertiary complex sed-iments (clays, sandstones and sands) as well as Cretaceoussediments (quartzite, sandstones, calcareous clays, marlitesand limestones). Volcanic rocks (basalts, phonolites andtuffs) are also found in the underlying complex. The overly-ing complex is comprised of a group of clays and sandy-clayswith variable occurrence of carbonates (Malkovsky, 1985).

The overlying complex’s border with the Quaternary sed-iments is problematic, especially in the immediate vicinityof the mountain slopes. The Quaternary sediments are madeup primarily of coarse-grained gravel, sandy gravel and clayswith crystalline fragments. The thickness of sediments variesfrom 0.1 m to 40 m. Increasing thickness is characteristic ofthe areas where the alluvial fans of former tributaries arefound. These alluvial fans contain mainly coarse grainedgravel, sands, loam and fragments of crystalline. The frag-ments of crystalline can reach up to one to five meters in size.Near the Krusne Hory Mountains, there are zones with soli-tary boulders within gravel debris (Zizka and Halır, 2009).

These sediments represent a large saturated collector,wherein saturation depends on grain size composition, thick-ness and the content of clay components. The saturation of

2The overlying and underlying complexes are defined accordingto their position relative to the coal seam

Nat. Hazards Earth Syst. Sci., 11, 1463–1473, 2011 www.nat-hazards-earth-syst-sci.net/11/1463/2011/

J. Burda et al.: Monitoring of recent mass movement activity 1465

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Figure 3 3

Landslide inventory map of the Jezeří protective pillar area. The range of the landslides is 4

based on geomorphic mapping and analysis of orthopohographs from 1987, 2000, 2003, 2006 5

and 2008. Dashed orange lines represent the approximate headscarps of the 2005 and 2007 6

slumps. The position of ERT profile is marked across the landslide "C". Underlying 7

orthophoto map is from 2006, when the mining front was just under the protective pillar. 8

Fig. 3. Landslide inventory map of the Jezeı protective pillar area.The range of the landslides is based on geomorphic mapping andanalysis of orthopohographs from 1987, 2000, 2003, 2006 and2008. Dashed orange lines represent the approximate headscarps ofthe 2005 and 2007 slumps. The position of ERT profile is markedacross the landslide “C”. The underlying orthophoto map is from2006, when the mining front was just under the protective pillar.

groundwater in the Quaternary sediments varies and dependson the factors listed. The gravels and sediments of alluvialfans have good permeability (up to 10−4 m s−1; Zizka andHalır, 2009).

From a hydrological point-of-view, the study site is locatedwithin the Bılina River catchment. The original territory wasdrained naturally bySramnicky Brook, which had to be redi-rected into artificial channels to facilitate the developmentof coal mining. Since the 1980s, the water from the entireSramnicky Brook catchment (22 km2) has been captured bya new channel, which diverts most of the water in a north-eastern direction towards the village of ernice. To divert wa-ter from the surface horizons, several drainage ditches werealso built into the talus cone near the former brook channel.

The Krusnohorsky Fault, which has a dominant structural-geological significance in this area, impacts the morphologyof the study area (Kopecky et al., 1985; Vilımek, 1994). Asoutheast watershed slope rises above the Mostecka Basinwith a very steep gradient – in some places more than35◦. Originally, a compact single watershed slope was sig-nificantly affected by erosion of the mountain brooks byperiglacial and nival processes during the Pleistocene, as wellas by large rockslides (Vane, 1960; Vilımek, 1995; Kalvodaet al., 1994).

Table 1. Values of absolute 3-D displacement of selected geodeticpoints.

Geodetic point Absolute 3-Dshift (2005–2009)

8010 291 mm8011 284 mm8016 445 mm8020 859 mm8026 776 mm8027 884 mm8029 10 317 mm8041 443 mm8079 4528 mm8119 322 mm

In the area where theCSA open-pit mine is adjacent tothe mountains, there is an anthropogenic slope created byoverburden benches. TheCSA open-pit mine side-slope wasprojected in the 1980s and, at present, is further modelled bystream erosion and mass movements.

3 Material and methods

Detailed geomorphic field mapping was the first step in theresearch. We located the current limits and distribution oflandslides, accumulation toes, scarps, erosion scarps andcracks. These basic slope-failures were mapped at all sitesat a scale of 1:2000 and using GPS. Landslide activity andspatial characteristics were studied using sets of aerial or-thophotographs from 1987, 2000, 2003, 2006 and 2008, andfrom aerial photos taken in June 2010 from on board Zlın-43,a civil aeroplane. Aerial orthophotographs were analyzed us-ing Geographical Information System (GIS), which made itpossible to reconstruct the studied mass movements as wellas temporal activity and to roughly estimate horizontal dis-placement.

In this study we attempt to we interpret the results ofgeodetic monitoring. The Leica TCR 2003 automated to-tal station monitors the positions of 45 stabilized geodeticpoints (reflecting prisms) at one-hour intervals. The reflect-ing prisms are attached to 3.5 m long stand pipes fixed withconcrete at a depth of 2 m. The automated total station ishoused in a protective cab situated in a geologically stablearea on the mined-out bottom of theCSA open-pit mine(Stanislav and Blın, 2007).

An ATR system (Automatic Target Recognition) measuresthe return time of the laser beam reflected by the reflect-ing prisms every hour. The system calculates the locationof the geodetic points and any resulting absolute (related tofour geodetic reference points, located on the walls of servicebuildings and towers outside the open-pit mine) and relative

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Fig. 4. ERT (electrical resistivity tomography) profile across the landslide “C” (A); Cross-sectional interpretation of ERT record (comparedwith rock cores from four nearest geological boreholes – see Fig. 2). Q – Quaternary colluvial deposits, T – weathered Tertiary clays(overlying complex), S – estimated position of Miocene sands (B).

(related to the previous location of the geodetic point) dis-placement is evaluated in 2-D and 3-D space. According toHampacher et al. (2008), the error in calculating the zenithangle is statistically insignificant and therefore only 3-D dis-placement is analysed in this study. Considering the dis-tances of 1400 to 1800 m, measurement error is about 20 to30 mm (Brown et al., 2007; Hampacher et al., 2008). Be-cause the measurement error is relatively large, it was neces-sary to adjust the methodology to define limits for geodeticmonitoring in this geomorphic research. We selected points,for which the 3-D shift reflects the mass movement’s activityand exceeds the measurement error. Two criteria were em-ployed in selecting such points: (1) continuous measure-ments throughout the 2005–2009 period; (2) values of abso-lute 3-D displacement, during this decade, exceed 250 mm.This threshold was determined empirically so as to enableselection of a representative number of geodetic points, forwhich values of 3-D displacements significantly exceededthe measurement error. Ten points were chosen from all ofthe monitored geodetic points (the values of abs. 3-D shiftare shown in Table 1). Either the absolute 3-D shift of theother geodetic points did not exceed 250 mm or their stabi-lization was destroyed (by landslide activity or heavy ma-

chinery) and the criteria of continuous measurements werenot met. The only exceptions are points 8079 and 8119,which were established in June 2006 and in October 2007,respectively, and have been monitored up to the present day.Therefore they have been included in this study.

Data for each geodetic point (position and annual 3-D dis-placement) were transformed into geo-objects allowing forthe spatial visualization of 3-D movements in GIS. Data wereinvestigated with the Surfer 9 software in order to examinespatial relationships between all the geodetic points (Stof-fel et al., 2005). Interpolations (Natural neighbour, grid size30×30 m) were performed including data from each of theyears (2005, 2006, 2007, 2008 and 2009).

The structure and character of the deep-seated landslidewas investigated using an electrical resistivity tomography(ERT) method. The research profile was performed acrossthe most active part of the landslide body. It was 186 m inlength with an azimuth of approximately 175◦. The surveywas carried out using a Resistar RS-100 instrument with aWenner-Schlumberger configuration and an electrode spac-ing of 2 m. The maximum depth of penetration was 20 m.Field data was processed using a 2-D inverse method inRes2DInv program (Loke and Barker, 1995), resulting in a



Table 2. Morphometric characteristics of active landslides “A” and“B” in the Western part of the protective pillar.

CharacteristicValue

landslide “A” landslide “B”

Length 800 m 920 mWidth 200 m 125 mTotal surface 58 000 m2 130 000 m2

Total volume* 400 000 – 950 000 m3 1.3–3 million m3

Maximum depth 13 m 10 mMaximum altitude (at crown) 281 m 272 mMinimum altitude (at foot) 154 m 99 mDifference of altitude 127 m 173 mAverage slope gradient 13◦ 10.5◦

∗ According to formulas in Malamud et al. (2004).

resistivity cross section that included topography. The ERTrecord has been compared with rock cores from four sur-rounding geological boreholes (JZ 19, JZ 42, JZ 93 and JZ111).

To confirm the existence of climatic influences, the 3-D shifts of selected geodetic points were compared withmonthly and daily precipitation. We used data sets from ameteo-station operated by the staff of Brown Coal ResearchInstitute (BCRI). This station is referred to as the “Jezerımeteo-station” (294 m a.s.l.) in the following text. It is lo-cated above the castle arboretum and so the impact of tor-rential rain as a triggering factor for mass movement can betaken into account. There are four hydrogeological monitor-ing boreholes in the area of interest. The hydrogeologicalboreholes are situated in the Quaternary sediments (boreholeJZ 212) and the crystalline complex (boreholes JZ 116, JZ117, JZ 182). Data from the boreholes were used to compilea map of Quaternary aquifers and groundwater flow.

4 Morphology and structure of landslides

Based on the field mapping and orthophotographic analysis,several slope deformations were identified. As Fig. 3 shows,the surface of these landslides has changed as a result of land-slide evolution but also due to dump construction.

Three active landslides “A”, “B” and “C”, which combineto form a landslide complex, were mapped in the westernpart of the study area. The landslide complex is situated ina non-reclaimed, anthropogenic slope and consists of twoearthflows and a deep-seated rotational failure. The mainmorphometric characteristics of both earthflows are shown inTable 2. The westernmost landslide “A” consists of three con-nected rotational sub-landslides, measuring more than 10 min thicknes. Only the west sub-landslide (from 2010) is ac-tive, the source areas of other two sub-landslides are com-pletely empty, because the material has been transported out(during 2006) and thus the slip surface is clearly visible.

Their toes joined 50 m lower on the slope and transformedinto an earthflow, which is continuous over all the overbur-den benches at the bottom of theCSA open-pit mine. Theformer accumulation toe (from 2006) is now buried by dumpmaterial. The active part is 800 m long and, at most, 200 mwide with a total surface area of 58 000 m2. According toMalamud et al. (2004), we estimated the total volume to bebetween 400 000 and 950 000 m3. The headscarp is 5 to 11 mhigh. Soil, colluvial sediments and weathered Tertiary com-plex sediments make up the visible outcrop in the headscarp.Several transverse cracks are located in the transport part ofthe landslide. The sharp – over 1.5 m high – linear side limitsare morphologically dominant. The landslide body contin-ues to be saturated with water and several springs have beenmapped in the source area. The water streams flow over thelandslides surface and accumulate in shallow ponds in de-pressions.

Landslide “B” is similar to landslide “A”; the material istransported in a large earthflow from a deep-seated sourcearea. The surface of this landslide is 130 000 m2, its maxi-mum length is 920 m, and its maximum width at the crownis 125 m. The headscarp has a typical amphitheatre shapeand only Quaternary sediments can be observed as outcrop.Several other headscarps (about 5 m high) are located lowerin the middle part of the slope where mainly Tertiary clay-stones comprise the outcrop. The landslide body has a hum-mocky shape and the middle part of the slope is covered byyoung vegetation of initial succession (birch – Betula pen-dula). In its lower part, the landslide body is saturated withwater accumulated in shallow ponds. Former accumulationtoes have been covered by dump material as a result of dumpadvancement during recent years.

The two earthflows (“A” and “B”) are divided by an indis-tinct ridge. The transported and accumulated material con-sists primarily of Quaternary debris but also includes weath-ered Tertiary clays. This fact, along with profiles over theheadscarps, indicates that the slip surface passes through Ter-tiary claystones and that this occurs not only at the interfer-ence of Quaternary and Tertiary sediments.

The third active landslide, “C”, is directly above land-slides “A” and “B” and is bound by a significant headscarpwith an apparent vertical displacement exceeding 1.5 m. Ac-tive cracks were mapped 6 to 10 m below the headscarp andthey limited rotated and sagged block. The minimal depth ofshear plane estimated from the ERT profile is 14 m (Fig. 4).The resistivities along the profile span an interval of 5 to800 ohm m. The 3rd iteration’s low RMS error of 3.5 % sup-ports the validity of the results. A relatively conductive (50to 200 ohm m) intermittent superficial layer in the northernpart of the section reaches a depth of 0.5 to 2.5 m and rep-resents the soil horizon. Below this layer there is lying anon-conductive (200–800 ohm m) material, corresponding tothe presence of sandy and stony proluvial deposits from theQuaternary Period. The base of these sediments is situatedat a depth ranging from 8 m (in the vicinity of stations 42



and 162) to 13 m (in the vicinity of stations 28 and 140).The substratum is made up of markedly conductive material(less than ten ohm m) formed by weathered Tertiary clayswith more sandy facies between stations 46 and 56. Two ac-tive cracks are manifested by sub-vertical conductive zonesdisrupting the high resistivity layer at stations 64 and 75.Presently, a non-active crack is indicated in the same wayat station 100.

On the west side, the landslide is sharply limited by atransverse 60 m long crack; conversely its eastern edge is notclear because the headscarp fades away. Longitudinal andtransverse cracks and scarps have been mapped all over theheadscarp of this landslide. According to Rybar (1996), theyoriginated in the 1990s.

In addition to this landslide complex, two smaller land-slides (both a rotational – “E” and a flow-like landslide –“D”) were identified from the orthophotographs (Fig. 3). Themovement of the flow-like landslide has also been recordedby geodetic point 8041 (total amplitude of displacement:443 mm), situated at the edge of the headscarp.

During 2007, a deep-seated slump developed in the east-ern part of the protective pillar. Pichler (2007) estimated theminimal volume of this landslide to be 110 000 m3, with aminimum depth of 11 m and width of 200 m. The crown ofthis deep-seated rotational landslide was at 221 m a.s.l. andthe toe at 210 m a.s.l. Many springs and streams were ob-served near the toe (E. Pichler, BCRI, personal communica-tion, 2010). Because it is an operational slope face, slumpsare routinely reclaimed immediately and it is not possible tomap the range of such slumps accurately, not even with or-thophotographs. As a result, it was impossible to map theexact limits of this slump (the assumed headscarp is shownin Fig. 3). The localization of the slump is also marked inFig. 5 (in the western part of the monitored area where thedisplacement of two points reached as much as 9 m in 2007).

5 Spatio-temporal analysis of landslide activity

Every part of the monitored area exhibited different valuesof 3-D displacements over the 2005–2009 period. Based onthe analysis presented in Fig. 5, we can define two zonesthat are characterized by the increased displacements values.Both zones coincide with the areas where slope deforma-tions have been mapped. The first, the southwest zone cor-responds to the site of the landslide complex. Based on thegeodetic method described in this article, five geodetic points(nos. 8010, 8011, 8020, 8041 and 8119) were selected for ananalysis of monthly 3-D displacement over the period from2005 to 2009 (Fig. 6). Overall, the measured values fluctu-ated between 30 and 50 mm. A slight increase in thresholdvalues occurred between July 2006 and February 2007. Ad-ditional increases were evident during November 2007 andduring the beginning of 2008, when a jump in measured val-

ues was evident at points 8020 and 8119. A subsequent in-crease followed during the first quarter of 2009.

The spatial-temporal characteristics of this landslide areacan be better estimated on the basis of orthophotograph setanalysis. Landslide “A” was identified first on the orthopho-tograph from 2006, but the “B” landslide can be observedfirst on the 2000 orthophotograph and its spatial evolution isevident during the following years. In the most recent period,this landslide has only been active in the lower parts of theslope, in the transport and accumulation area.

The second zone of increased 3-D displacement valuesduring the 2005–2009 period, is situated in the eastern partof the protective pillar. This part of the protective pillarwas affected by deep-seated slumps in 2005 and 2007. Asin the previous area, we chose several geodetic points tocarry out an analysis of monthly 3-D displacement. Pointsno. 8016, 8026, 8027, 8029, and 8079 were selected. Al-together, the values fluctuated between 20 and 30 mm dur-ing the 2005–2009 period and such fluctuations are withinthe range of measurement error. Nonetheless, we can reli-ably identify months where landslide developments and sig-nificant shifts affected the monitored points. These monthsare at the end of 2005 and the beginning of 2006. Move-ments in September and November 2006 indicate a progres-sively evolving landslide. On 10 February 2007, primarymovement activity of the landslide was observed in the mid-dle part of the SE-facing slope. This trend is similar tothe previous case, but the absolute displacements reachedmuch larger values (point no. 8029:9352 mm month−1, pointno. 8079:4154 mm month−1). The activity was captured byeight geodetic points, but only points 8016, 8026, 8027,8029 and 8079 were not destroyed during the landslide ac-tivity. The evolution of this slump has been reported since2006, when measured displacements reached as much as 1 m(Fig. 5).

6 Landslide triggers

The immediate triggering factor for the landslide activity inthe study area is the water saturation of landslide material,due to a combination of high cumulative rainfall and snowmelt water that results in water table increase (Fig. 7). In-creases in measured values of 3-D shift almost always co-incide with sharp increases in the height of the water table.This is quite evident in the landslide on the SW-facing slopefrom 10 February 2007, where landslide activity was causedby long-term rainfall culmination (cumulative 118 mm vs. anaverage 22 mm), which occurred during the 2007 snow-thawperiod. At the end of January and into February, a sudden in-crease in average daily temperatures by more than 10◦C, oc-curred, leading to rapid snow melt and water table increase.The maximum daily temperature varied between 4.5 and 9◦Cfrom 29 January through 9 February 2007. A similar trendof revival displacements, depending on increased water table



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Figure 5 3

Amplitudes of annual 3D displacements. The patterns have been generalized based on 4

interpolations. 5

Fig. 5. Amplitudes of annual 3-D displacements. The patterns have been generalized based on interpolations.

levels, can be observed at the beginning of every year as wellas during November 2007 (see Figs. 6 and 7).

In the same period of above-average rainfall during the be-ginning of 2008, an acceleration of movements was observedon the deep-seated landslide complex in the SW-facing slope.The most significant peak in movement (more than 150 mmper month) was observed with a one year delay on the SE-facing slope, but the landslide activity continues up to thepresent time.

7 Discussion

Information about groundwater flow, the configuration of thecolluvial mantle as well as geodetic monitoring data and cli-matological data could further improve the prediction of spa-tial landslide hazards and the precision of geotechnical mea-sures, thus minimizing any potential damage.



Fig. 6. Monthly 3-D displacements of selected geodetic points (top – SE facing slope, middle – SW facing slope). Cumulative deviationsfrom average monthly rainfalls (bottom): above-average periods – blue line; subnormal periods – red line (Burda and Vilımek, 2010).

Fig. 7. Fluctuations of water table and water temperature in the JZ 212 borehole. Red marks indicate increasing groundwater level in thesame period when values of 3-D shift increased (taken from: Chan et al., 2009).

The geodetic monitoring system described above was de-signed as an early warning system to prevent possible dam-age to equipment during mining activities. The main disad-vantage of this method is its measurement error, which de-pending on the distance, can increase to 20 or 30 mm. In par-ticular, data from the early months of measurement shouldbe considered with restraint, as the data is incomplete and

the values of monthly shifts could be error prone as a resultof the initial stages of measurement (see Stanislav and Blın,2007). Therefore, the increased values of 3-D shift from thefirst months of 2005 cannot by reliably interpreted. Due tothe appropriate selection of the geodetic points, we have beenable to find points that accurately reflect the landslide activ-ity. The treshold of absolute 3-D displacement of 250 mm is



sufficiently exaggerated to enable us to state that it reliablyreflects mass movement activity.

Another disadvantage of the geodetic monitoring is theconsiderable distance between selected points and thus, thelow spatial coverage of area monitored with geodetic points.This fact does not allow the optimal placement of geodeticpoints, relative to the evolving landslide. Consequently, weestimated the velocity of the earthflows “A” and “B” on thebasis of our analysis of geodetic points located mainly at theedges of the landslide bodies. Even so, these geodetic pointsare influenced by the landslide activity and so they showedcontinuously increased values of displacement. The actualvelocity within the earthflow, however, is higher than themeasured values. The fact that minimal values of displace-ment were measured on the southwest-facing slope from2005 to 2007, despite the fact that according to orthopho-tographs and field mapping, the landslides evolved there canalso be explained by the low density of geodetic points. Dueto the nature of landslides, which exhibit the characteristicsof a flow, it is not possible to stabilize geodetic points in thelandslide bodies. Existing geodetic points which were in-stalled in the landslide body were destroyed a short time af-ter the main activity. Therefore, they could not be used forlong-term analysis of landslide activity.

There are significant insufficiencies regarding this geode-tic method when trying to analyse flow-like landslide dynam-ics. In general, this study shows that combinations of themethods used (geodetic monitoring data, geomorphic map-ping, orthophotograph analysis, utilization of climate and hy-drogeological data and geophysical investigation) can pro-vide a powerful tool for the analysis of mass movement dy-namics and their triggers in a significantly anthropogenic-influenced area.

The findings demonstrate that the landslides are triggeredby precipitation infiltration and the resulting water table in-crease. Rybar and Novotny (2005) and others (Rybar, 2006;Burda and Vilımek, 2010) have also discussed the influ-ence of climatic factors in landslide occurrence. In general,they suggest that deep-seated landslides have occurred in thestudy area due to culmination of long-term precipitation withup to two years delay. The rotational landslide under Mt. Jez-erka (Rybar and Novotny, 2005) is a typical and often-citedexample of such slope failure (its depth was 50–60 m with atotal volume of about 3 million m3). The main movement ac-tivity occurred in summer 1983, one and half years after therainfall culmination. In contrast, the deep-seated landslidesstudied herein are evolving with no or minimal delay afterlong-term precipitation culminations.

This can be explained by a combination of two factors:(1) The study site is situated in the foreground of the mouthof the Sramnicky Brook’s valley; (2) Recent slope failureshavecaused the slope to relax, which in turn has led to eas-ier deep-soaking of rainfall water or snow-thaw water fromthe entire catchment area. Both parts of the protective pillar,where increased values were measured, have been affected

by recent deep-seated landslides. The SE-facing slope col-lapsed completely in June 2005 (before monitoring began)as a result of a large deep-seated landslide, the volume ofwhich was about 7 million m3 (Rybar and Novotny, 2005;see in Fig. 3).

The first cracks were mapped at the site of the landslidecomplex back in 1952 (Spurek, 1974, BCRI archive). Afterthis, part of the slope was undermined by the Konv under-ground mine (see in Fig. 3). The reactivation of these crackshas been evident since June 1990 (Rybar et al., 1996), withan average annual vertical drop of 28 mm in the body of land-slide “C” (Pichler, 2007).

Although the area has been drained artificially, numeroussprings in the landslide complex show that the triggeringarea is permanently saturated with groundwater. The lowestdrainage ditch was even interrupted by landslide “A”, duringApril 2010. Apparently, water gets to the source area fromdeeper horizons. This theory was also confirmed by an ERTinvestigation that revealed markedly conductive material inthe Tertiary complex. It is probable that the extremely con-ductive part of these clays, situated at an average depth of14 to 15 m, is conditioned by weathered and water-saturatedclays and represents an assumed water-bearing shear plane.The system of groundwater flow is affected by the configu-ration of the Quaternary structures and the crystalline roof.The source area corresponds to the mountain slopes and in-flows of groundwater work their way through the disruptedcrystalline roof with Quaternary sediments. The water ta-ble of the Quaternary aquifer is dependent entirely on pre-cipitation and on water flowing from the adjacent slopesof the Krusne Hory Mountains and from the catchment ofSramnicky Brook. The processed model of groundwater flowdirections (see in Fig. 3) exactly matches the actual locationsof observed water springs. The tributaries of these watersflows introduce complications and they are the main sourceof stability problems.

Despite detailed geomorphic mapping and the ERT inves-tigation, the structure of landslide “C” is still not fully clear.The ERT investigation was limited by the maximum depth ofpenetration which was 20 m. Ground water flowing along theinterference of Quaternary and Tertiary sediments was reli-ably identified, but the maximum depth of the shear planecould be much greater (possibly up to 60 m as is the depth ofthe coal seam). In this case, it could be a slow moving, block-rotated, deep-seated failure similar to slope failures occurringin the Flysh Belt in the Czech Republic (Baron et al., 2004).

8 Conclusions

This study shows that large earth-flows and slumps evolvedin specific anthropogenic relief near the foothills of theKrusne Hory Mountains. Specific geological, geomor-phological and anthropogenic conditions have caused massmovements here to be similar to the Flysh Carpathians



region, where the magnitude and dynamics of mass move-ments are greatest in the Czech Republic (Klimes et al.,2009).

Two zones of high 3-D displacement values were found onthe basis of geomorphic mapping, aerial orthophotographsand geodetic monitoring data analysis. The landslide com-plex, consisting of slow moving, deep-seated rotational fail-ure and two earthflows, was mapped in the western part ofthe study area. Landslide mechanics in this part of the pro-tective pillar are characterised by sliding slowly passing intoflowing; however, due to measurement error, it is impossibleto detect initial creep. The eastern part of the protective pillarwas largely reclaimed during 2007 and, consequently, it wasnot possible to map slope failures from 2005 and 2007.

All of the selected geodetic points are usually in motionin the beginning of the year (January through March). In as-sessing the conditions in which the mass movements are de-veloping, it is necessary to consider the combined influenceof several factors. The landslide activity is triggered by themutual effects of high cumulative precipitations and snowmelt water. This results in high water tables and increasedpore water pressure eventually leading to the mobilizationof weathered claystones and overlaying Quaternary colluvialand alluvial sediments.

The fact that these deep-seated landslides occurred withno or minimal delay following precipitation culmination(Fig. 6) indicates that water is quickly soaking to deeper hori-zons. This is apparently the consequence of the thicknessof the colluvial mantle, saturated by ground water from theSramnicky Brook catchment and former slope failures whichoccurred in 1952 and 2005 and led to the relaxation of theslope.

Generally speaking, detailed field mapping in this area ofsignificant anthropogenic influence is difficult and so most ofthe landslides could only be mapped from orthophotographs.Groundwork, reclamations and dump advancing led to sig-nificant changes in the landslide surface and to the burial offormer accumulation toes. Therefore, the estimated landslidecharacteristics presented above are only indicative and the to-tal volume and surface area could actually be higher.

In subsequent years, the results of this research will besupplemented with three additional ERT profiles and thedynamic of the landslide complex will be monitored by aterrestrial LIDAR system from the beginning of 2011 on-wards. The results will be used for planning reclamation andgroundwork following the end of coal mining in the area.

Acknowledgements.The research was supported by these projects:

– Grant Project of Charles University in Prague (GAUK)No. 155610: “Analysis of recent mass movement distributionand their dynamic in the Jezerı area, Krusne Hory Mountains.”

– MSMT 1M06007: “Research Centre for Integrated System ofSide Products Use from Energy Sources Exploitation, Prepa-ration and Processing”

– Grant SVV-2011-261 201: “Research on the physical-geographical changes in the natural environment of the Earth”

Edited by: A. GuntherReviewed by: I. Baron and another anonymous referee

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